Field of the Invention
The present invention relates to an ingot, a silicon carbide substrate, and a method for producing the ingot, more particularly, an ingot formed of silicon carbide, an silicon carbide substrate obtained from the ingot, and a method for producing the ingot formed of silicon carbide.
Description of the Background Art
In recent years, in order to achieve high breakdown voltage, low loss, and the like in a semiconductor device, silicon carbide has begun to be adopted as a material for the semiconductor device. Silicon carbide is a wide band gap semiconductor having a band gap larger than that of silicon, which has been conventionally widely used as a material for semiconductor devices. Hence, by adopting silicon carbide as a material for a semiconductor device, the semiconductor device can have a high breakdown voltage, reduced on-resistance, and the like.
A silicon carbide ingot is produced by, for example, growing a silicon carbide single crystal on a seed substrate using a sublimation-recrystallization method. In the grown crystal of this silicon carbide ingot, stress, strain, and the like are generated. They may cause generation of crack in the ingot or a silicon carbide substrate obtained by cutting the ingot. To address this, Japanese Patent Laying-Open No. 2012-250864 discloses to relax stress or strain in a crystal by reducing a concentration gradient of metal atoms in a growth direction of an ingot, for example.
In Japanese Patent Laying-Open No. 2012-250864 described above, the stress or strain in the crystal can be relaxed to some extent, but it is difficult to sufficiently suppress generation of crack in the ingot and the silicon carbide substrate obtained by cutting the ingot.